1. Field of the Invention
The present invention relates generally to recording devices and, more particularly, to a laser driver that produces a write strategy using a binary record signal which is recorded on a recording medium and a record, and an optical disk system in which data can be recorded and which includes the laser driver.
2. Description of the Related Art
In recent years, a recording speed at which data is recorded on an optical disk has improved. When modulated data is recorded on the optical disk at a high speed, a laser control signal must be transmitted to a laser driver in order to realize a write strategy, that is, a recording waveform inferred from the record data. Techniques for transmitting the control signal include a technique of transmitting a record data signal resulting from modulation of data, for example, a non-return-to-zero inversion (NRZI) signal, and a recording clock to the laser driver. Consequently, a write strategy is produced based on the received NRZI signal and recording clock within the laser driver (refer to, for example, Japanese Unexamined Patent Application Publication No. 11-283249).
According to the technique, the laser driver produces the write strategy from the NRZI signal. Therefore, the laser driver must strobe the NRZI signal received from a digital signal processor (DSP) according to the recording clock so as to verify whether the NRZI signal assumes logical 0 or 1.
When the recording clock is used to strobe the NRZI signal, a setup time required until the logical state of the NRZI signal is finalized prior to strobing and a hold time required until data fetch is completed after the completion of the strobing must be preserved. Unless these times are preserved, strobed data cannot be finalized and a recording error may occur. For example, assume that the laser driver having the setup time set to 0.8 ns and the hold time set to 0.6 ns is used to record data on a DVD-R/RW disk in decoupled speed mode. In this case, since the time of one cycle of the recording clock is 3.8 ns, the phase of the NRZI signal relative to the recording clock must be controlled so that the edge of the NRZI signal will come during 2.4 ns calculated by subtracting the setup time and hold time from 3.8 ns.
Moreover, the phase of the NRZI signal relative to the recording clock is affected by a phase error caused by a modulating device, the property of a transmission line, a change in the properties of the laser driver depending on the internal temperature and supply voltage of a pickup head, and the jitters of the NRZI signal and recording clock. The phase of an NRZI signal relative to a clock must be controlled with a sufficient phase margin ensured.
Methods for avoiding the above problems include a method employing a variable delay circuit that can delay the NRZI signal and recording clock after or immediately before the NRZI signal and recording clock are transferred to the laser driver, and a circuit that can monitor the phase relationship between the NRZI signal and an internal strobing clock. According to the method, for example, a microcomputer that controls a system changes the magnitude of a delay to be produced by the variable delay circuit, and monitors a monitor signal. The microcomputer thus adjusts the magnitude of a delay to be produced by the variable delay circuit so that the phase relationship between the NRZI signal and recording clock will be optimized.